Incorrect Or Missing Interface Level Reading - Emerson Rosemount 3308A Reference Manual

Reference Manual
00809-0100-4308, Rev CA
Symptom
Level stuck in measuring range.
Level stuck in empty.
Level fluctuations (a couple of inches).
6.3.2

Incorrect or missing interface level reading

Symptom
Incorrect Interface Level reading.
Missing Interface Level reading (reported
as NaN).
There are two products in the tank, but
only the product surface or interface is
detected.
There are two products in the tank, but
no readings are reported.
There is only oil in the tank but the
transmitter reports water.
There is only water in the tank but the
transmitter reports oil.
Service and Troubleshooting
PRELIMINARY
Possible cause and recommended actions
May be caused by a disturbing object in the tank. Read the Echo
Curve and adjust Thresholds, see
page 94.
Check if the probe is bent and in contact with the tank wall. This
contact causes a false echo reading.
Heavy coating or contamination on the probe. Clean the probe.
Thresholds may be too high, see
page 94.
There is too much disturbing noise in the tank (from foam,
splashing etc.). Set the Performance Mode to High to get a stable
measurement signal, refer to
page 106.
There are rapid level changes in the tank. Select a faster Update
Rate, refer to
Thin oil layer on top of water that is sometimes detected,
sometimes not. Set the Peak Detection Method to Threshold
Intersection to improve the stability of level measurements in
such applications. Refer to
Possible cause and recommended actions
The Upper Product Dielectric Constant is not correct, see
product dielectric constant" on page
Air gap is too big when the Measurement Mode is set to Interface
Level with Submerged Probe. Reduce air gap or switch the
Measurement Mode to Product Level and Interface Level.
The Measurement Mode is set to Product Level. Set Measurement
Mode to Product Level and Interface Level, refer to
mode" on page
The Interface Peak is difficult to detect, because the bottom
product has a low dielectric constant, or the signal is attenuated in
the upper product. Check Thresholds. For more information, see
"Example 2: Interface peak not found" on page
The upper product is too thin to be detected. No action is needed.
See "Interface measurements" on page 119
interface thickness for different probe types.
Check Thresholds, see
Check Thresholds, see
Check Thresholds, see
Make sure the Typical Interface Condition is set to Layer at the
bottom (thin) if you typically have a thin layer at the bottom, see
"Typical interface condition" on page
Check Thresholds, see
Make sure the Typical Interface Condition is set to Layer on Top
(Thin) if you typically have a thin layer at the top, see
interface condition" on page
Service and Troubleshooting
"Adjusting thresholds" on
"Adjusting thresholds" on
"Noise or weak surface echoes" on
"Configure update rate" on page
"Resolving thin oil layers" on page
163.
163.
"Adjusting thresholds" on page
"Adjusting thresholds" on page
"Adjusting thresholds" on page
164.
"Adjusting thresholds" on page
164.
August 2017
67.
100.
"Upper
"Measurement
97.
for minimum
94.
94.
94.
94.
"Typical
91